Flow restrictors having no moving parts are known for incorporation in the conduits or passageways of transmission control systems. These flow restrictors provide an accurately metered and substantially constant fluid flow rate under given pressure conditions and are particularly useful for controlling the rate of pressure rise to the annular pistons associated with the clutches and/or brakes of present day transmissions.
The Lee Company of Westbrook, Connecticut offers a series of cascade restrictors of generally cylindrical disc-like shape having single ingress and egress passages and a tortuous internal path for the fluid. The minimum passage size in the fluid path of such restrictors is relatively large, for example about the equivalent of a cylindrical opening having a diameter of 1.52 mm (0.060"), and yet the restrictor acts as if it had a fluid flow resistance level equivalent to a simple orifice of much smaller diameter, for example about 0.51 mm (0.020"). The major advantage is that a simple orifice of very small diameter might be plugged by a single grain of sand, so that it is undesirable to use very small diameter orifices in the transmissions of vehicles. These cascade restrictors are modularized so that one, two, three or even more individual units can be placed together in a cylindrical stack to provide the equivalent resistance to progressively smaller simple orifices.
The major problem with presently available flow restrictors is that they are constructed and manufactured in such a way that they are too expensive. Specifically, at least some cascade restrictors are currently constructed by initially removing material from thin steel sheet material or shim stock. The individual layers are then stacked up forming a series of small cylindrical discs with the material removed from the sheet material forming the internal tortuous path. End plates with ingress and egress passages are added to the stack to form a single modular unit or stage and the individual sheet material layers are collectively secured together such as by welding or the like. This is wasteful and time consuming.
Another fluid flow restrictor assigned to The Lee Company is disclosed in U.S. Pat. No. 3,323,550 issued to L. Lee II on June 6, 1967. However, relatively expensive machining methods are again utilized in that construction.
The present invention is directed to overcoming one or more of the problems as set forth above.